The rules state:At the end of each player's turn, once troop redeployment is over, the Necromancer spawns new Ghosts onto the Island.

Is this a requirement? Can the Necromancer stockpile the souls in the well for a turn or two? If so, the Necromancer could spawn them at the end of his own turn...

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Also I have a clarification that may be helpful for someone else (the English wording chases its tail a bit.)
The rules state:For each set of 4 tokens in the Well of Souls (removing Ghost tokens first), 1 new Ghost is taken from the Necromancer's Reserve and placed on Necromancer Island. Any Ghost token removed from the Well of Souls to spawn a new Ghost onto the Island is placed back in the Necromancer's Reserve.

All this means is that you don't have to use the top 4 souls to spawn a Ghost. Keyaerts wants you to clear the Well of your Ghosts so that they are available to purchase. That way you don't get stuck trying to buy your last Ghost(s) on your turn, and win, but it's stuck at the bottom of the well. This rule is just stating that there's no top & bottom to the Well, or a specific order in which souls come out of it.

It DOES NOT MEAN that you can spawn Ghosts directly to the board from the Well if they are among the 4 souls being brought out of it at the end of someone's turn.

The "Necromancer's Reserve" is the tray. I don't know why they don't call it that. It's not some extra tile you should've received or some imaginary theme park for Ghosts. So, spawned Ghosts and purchased Ghosts all ALWAYS come from the tray, never the Well.

One final clarification...What happens when the Pygmies are on the board at the same time as the Necromancer? Do Pygmy tokens NOT go to the well? (OR) After the recovery roll, can Pygmies snatch tokens back out of the Well of Souls?

This one has come up each time a new player hits this scenario. I believe the ruling is this: The rules clearly state that the Pygmy tokens come FROM THE TRAY. So, if they are still stuck in the Well, there's no way the Pygmy player can benefit from their racial ability. If they aren't in the tray yet, they can't be reclaimed yet.
This is why the above point about no-bottom-or-top-of-the-well is so vital to establish! It affects the availability of tokens for the Necromancer AND the Pygmies. (The Necromancer--if he chooses which souls to use for spawning Ghosts--can really cripple the Pygmy player. I guess this would also be true of Skeletons and Sorcerers, assuming they were ever able to get that much traction on the board.)